Enable DH tests

In master, the 'dh' command is gone, so use 'dhparam' instead to
determine if we're compiled with DH.

Also, set "@SECLEVEL=1" for the weak DH test, so that it actually
passes.

Reviewed-by: Dr Stephen Henson <steve@openssl.org>
diff --git a/test/ssltest.c b/test/ssltest.c
index f640d92..26cf96c 100644
--- a/test/ssltest.c
+++ b/test/ssltest.c
@@ -1429,7 +1429,8 @@
     }
     /*
      * Since we will use low security ciphersuites and keys for testing set
-     * security level to zero.
+     * security level to zero by default. Tests can override this by adding
+     * "@SECLEVEL=n" to the cipher string.
      */
     SSL_CTX_set_security_level(c_ctx, 0);
     SSL_CTX_set_security_level(s_ctx, 0);